Aging and fatigue of ferroelectrets: combined experimental and theoretical study

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The objective is a combined experimental and theoretical study on the stability of the electromechanical properties of porous ferroelectrets. In particular, three different mechanisms which play influential roles in aging and fatigue of the ferroelectrets will be revealed. Firstly, the viscoelastic effect appears in both the porous polymer and the blocking bulk polymer. It leads to time- and temperature-dependent mechanical behavior of the material and thus influences the electromechanical properties of the ferroelectrets. To characterize the viscoelastic behavior uncharged ferroelectrets with different microstructure at different temperatures will first be experimentally and numerically studied. The gained knowledge will be then passed on to the study of charged ferroelectrets. Secondly, the interface charge decays with time due to the conductive relaxation of the porous polymer, i.e. the diffusion/drifting of charge carriers through the dielectric media. This conduction-induced discharge behavior is also temperature dependent. Since the interface charge is essential for the piezoelectric effect of ferroelectrets, the conduction-induced discharge plays an important role in the stability of their electromechanical property. Experimental investigations and theoretical model to take this discharge into account are planned. Thirdly, the interface charge can also change during the mechanically loading, when the electric field reaches the electric breakdown field due to configuration change. This breakdown-induced discharge is more likely to happen when the interface is charged on a high level and/or the mechanical loading is large. These three effects will be investigated in the present project through combined experimental and theoretical studies, results of which should guide the design of long-term and electromechanically stable ferroelectrets.